S1P1 receptor agonists have been shown to possess at least immunosuppressive, anti-inflammatory, and/or hemostatic activities, e.g. by virtue of modulating leukocyte trafficking, sequestering lymphocytes in secondary lymphoid tissues, and/or enhancing vascular integrity. Accordingly, S1P1 receptor agonists can be useful as immunosuppressive agents for at least autoimmune diseases and disorders; inflammatory diseases and disorders (e.g., acute and chronic inflammatory conditions), transplant rejection, cancer, and/or conditions that have an underlying defect in vascular integrity or that are associated with angiogenesis such as may be pathologic (e.g., as may occur in inflammation, tumor development, and atherosclerosis) with fewer side effects such as the impairment of immune responses to systemic infection.
The sphingosine-1-phosphate (SIP) receptors 1-5 constitute a family of G protein-coupled receptors containing a seven-transmembrane domain. These receptors, referred to as S1P1 to S1P5 (formerly termed endothelial differentiation gene (EDG) receptor-1, -5, -3, -6, and -8, respectively; Chun et al., Pharmacological Reviews, 54:265-269, 2002), are activated via binding by sphingosine-1-phosphate, which is produced by the sphingosine kinase-catalyzed phosphorylation of sphingosine. S1P1, S1P4, and S1P5 receptors activate Gi but not Gq, whereas S1P2 and S1P3 receptors activate both Gi and Gq. The S1P3 receptor, but not the S1P1 receptor, responds to an agonist with an increase in intracellular calcium.
In view of the growing demand for S1P1 agonists useful in the treatment of S1P1 receptor-associated disorders, the compound (R)-2-(7-(4-cyclopentyl-3-(trifluoromethyl)benzyloxy)-1,2,3,4-tetrahydrocyclopenta[b]indol-3-yl)acetic acid of Formula (Ia):
has emerged as an important new compound, see PCT patent application, Serial No. PCT/US2009/004265 hereby incorporated by reference in its entirety. Accordingly, new and efficient routes leading to (R)-2-(7-(4-cyclopentyl-3-(trifluoromethyl)benzyloxy)-1,2,3,4-tetrahydrocyclopenta[b]indol-3-yl)acetic acid of Formula (Ia), salts, and intermediates related thereto are needed. The processes and compounds described herein help meet these and other needs.